Polyfill JavaScript Array.prototype.find for older browsers (e.g. IE 10, IE 11)

array_find.js

if (!Array.prototype.find) {
        Array.prototype.find = function(predicate) {
            if (this == null) {
                throw new TypeError('Array.prototype.find called on null or undefined');
            }
            if (typeof predicate !== 'function') {
                throw new TypeError('predicate must be a function');
            }
            var list = Object(this);
            var length = list.length >>> 0;
            var thisArg = arguments[1];
            var value;
            
            for (var i = 0; i < length; i++) {
                value = list[i];
                if (predicate.call(thisArg, value, i, list)) {
                    return value;
                }
            }
            return undefined;
        };
    }

Why do you use list.length >>> 0 and return undefined?